1. Field of the Invention
The present invention relates to a method and device for detecting flickers in television pictures.
2. Description of the Related Art
In the production of films and television programs, there is an editing technique of alternating two different scenes at one-frame intervals or at short time intervals to produce special effects. The similar effects may be achieved by a stroboscopic illumination. These scenes appear as striking flickers on the television screen and a viewer sensitive to the flickers of light, when watching these scenes, may have a fit or convulsion or complain about other physical anomalies.
To prevent such troubles, it is common practice to detect extreme flickers and, when they are found to exceed a warning level, issue an alarm to production staffs.
An example conventional technique for detecting flickers considers a flicker in terms of a change of scene or a cut and, when a series of such changes or cuts occur, decides that a flicker has occurred. If we let (i,j) stand for a spatial position in a present field or frame, A.sub.n (i,j) for its brightness, and A.sub.n-1 (i,j) for the brightness of the same position one field or one frame previous, this technique evaluates a change of scene or a cut as expressed below: ##EQU1## where T is an appropriately set threshold value. That is, the absolute value of a field difference or frame difference at the same position spanning successive fields or frames is integrated within the field or frame. When the integrated value exceeds a predetermined threshold, it is decided that the scene has been changed. When this change of scene, or cut, occurs successively, it is decided that a flicker is produced.
The conventional technique has a drawback that when there is a rapid motion in a scene or the scene is switched through fading, the field difference or frame difference occurs successively resulting in a false detection of flickers. Further, when one wishes to detect flickers down to small magnitudes, the value of T in the equation (1) needs to be set to a small value, making the motions in a scene and the overlap switching more likely to be detected as flickers undesirably.